Study On Hybrid Joining Process Of Stainless Steel And Magnesium Alloy

Low density, high specific strength, high specific elastic modulus and highdamping shock absorption make magnesium alloy play an important role in the field ofaerospace, machinery, petroleum and so on. Good mechanical and thermo-electricproperties, corrosion resistance, low price make the stainless steel industry’s mostwidely used alloys. In order to take advantage of the performance of magnesium alloyand stainless steel, they usually need to be joined together. However, due to the hugedifferences in physical, chemical and mechanical properties between them, it is difficultto join sound by using traditional or single joining technology.In view of those problems above, a solid-state diffusion and transient liquid-phase(TLP) hybrid bonding method was proposed to join the stainless steel and themagnesium alloy with a copper interlayer. First, the stainless steel and copper interlayerwere sound bonded at850℃, with the help of pulse-pressuring diffusion bonding(PPDB) and surface self-nanocrystallization (SSNC). Then the TLP was carried out tojoin the304L/Cu/AZ31at a lower temperature and the joining process was studiedsystematically. Microstructure observation, micro-hardness testing, scanning electronmicroscope (SEM) observation, energy dispersive spectroscope (EDS) and X raydiffraction (XRD) analysis were employed to investigate the structure and performanceof304L/Cu/AZ31joints.The results show that diffusion bonding technology of stainless steel and copperwas optimized observably by combining PPDB and SSNC. The optimized parameterswere gained as follows: bonding temperature being850℃, pulse pressure being5～20MPa, pulse pressuring times being600cycles with a frequency of0.5Hz. The jointstrength under the optimum condition was257.5MPa, which is93.5%of that of a Cubar (~275MPa). The mainly phase on the bonding interface was Fe-Cu solid solution.The joint strength of304L/Cu/AZ31achieved34.7Mpa when the welding parametersof TLP are set as: bonding temperature T=520℃, preserved time t=9min, pulse pressureP=2～5MPa, pulse pressuring times n=150and frequency f=0.5Hz. The fractureoccurred between the magnesium alloy and copper interlayer, and the mainly Cu-Mgcompounds were Cu2Mg and CuMg2. A layered structure of304L/Fe-Cu diffusionlayer/Cu/Cu-Mg-based intermetallic compounds/AZ31was present in the bondingregion.